EWP Blog – Page 43 – Spring Experiments & Beyond

Low Probabilities of LightningCast Despite Observed Cloud to Ground Lightning Within Trailing Anvil / Stratiform Region

Posted in DSS, LightningCast, SPG2023 on June 15, 2023 by Kevin Thiel.

While providing (fictitious) DSS for a grass fire near Meade, KS on June 15, 2023, LightningCast was utilized in notifying the onset of lightning within 10 miles of the DSS site as a line of severe thunderstorms approached. Additionally, consideration was given to the potential for lightning cessation over the site in an effort to give information on potential for the “all clear.”

Figure 1.

LightningCast within the trailing anvil portion of the squall line steadily dropped off within the trailing stratiform region. However, these probabilities decreased when cloud to ground lightning was still being observed, with even some strikes occurring in probabilities less than 10%. This can be seen in Figure 1 in the far left hand portion of the animation with CG icons occurring within and outside of the lower contours of LightningCast.

This significantly lowered confidence in tracking the lower probability contours to give an estimated time of cessation.

Here was the DSS message sent at around 21:45 UTC:

As of 4:45 pm CDT, severe thunderstorms are 20 miles west of your site, and continue to approach your site. There is a very high chance these storms remain severe by the time they reach your site, currently expected between 5:15 pm and 5:45 pm CDT, bringing very strong winds over 70 mph out of a direction ranging between northerly to westerly, heavy rainfall, and frequent lightning. We still cannot rule out the potential for a brief tornado and large hail, although the chance for a tornado and hail is much lower than previous hazards mentioned.

Because of the approaching thunderstorms, the chance for lightning to occur within 10 miles of your site within the next hour (5:45 pm CDT) is over 99%.

It is worth noting that even after severe hazards associated with this line of thunderstorms have ended, there will remain over 75% chance of lightning over your site for an additional 1-2 hours, along with the potential for continued gusty winds over 20 mph ranging out of the southeast to northeast.

– 0SMBLSN

Using Satellite to Aid in Defining Areas of Concern for Graphical Messaging

Posted in LightningCast, SPG2023 on June 15, 2023 by Kevin Thiel.

June 15, 2023 – Role playing as DDC, a colleague and myself were tasked with creating a public graphic for a near term forecast regarding the location and timing of the potential for severe thunderstorms and associated hazards.

There was ongoing severe convection within the western half of the CWA by the start of our shift. After going through a quick forecast process and mesoanalysis, it was determined that a prime environment for either additional or sustained severe convection was spreading into the southern and eastern portions of the CWA.

Shortly thereafter, satellite gave indications of convective initiation in the vicinity of a triple point of a surface low. Satellite imagery and products that gave indication of building, infant convection included Day Cloud Type RGB and LightningCast via GOES-West Mesosector 1.

Figure 1.

Day Cloud Type RGB was used to track the vertically growing Cu, while using the Time of Arrival Tool and knowledge of the environment to estimate the spatiotemporal extent ( orange dashed outline) of where severe convection would occur within the next two to three hours, as displayed in Figure 1. Additionally, LightningCast was used to build confidence in where convection was growing and tracking, aiding in defining this area of concern.

Figure 2.

When comparing this to radar reflectivity (Figure 2.), radar was devoid of robust convection in the growing area of concern. Thus satellite proved useful in providing further lead time in defining the area of concern as well as when to start graphic creation. While we opted to not show satellite imagery for public consumption (satellite imagery can be distracting and/or misinterpreted when messaging severe hazards and impacts), it was crucial in the development stage of graphic creation, particularly defining areas of growing concern.

Here was the graphic we created:

How did it pan out? Pretty well, actually:

Figure 3 shows an animation of MRMS Composite Reflectivity and ProbSevere through the window of forecast hazards to help illustrate how severe convection developed between 20:00 UTC through 22:15 UTC within DDC during the period of concern.

Additionally, here are the SPC reports between 20:00 UTC to 22:15 UTC within DDC during the period of concern, including a measured 88 mph wind gust at 21:30 UTC within Seward County:

– 0SMBLSN

PHS and SPC Mesoanalysis, 0-6km Shear

Posted in PHSnMWnABI, SPG2023 on June 15, 2023 by Kevin Thiel.

I noticed that there was a big difference in 0-6km bulk shear values between the PHS MesoA and SPC Meso page. The gradient was similar but not the values. Highest values from the PHS MesoA was in the mid 30s. Highest values on SPC’s page was in the 60s at around 20z.

– SATGLM_84

SHV Feedback for 6/14 and some feedback from LZK CWA

Posted in NUCAPS, OCTANE Speed Sandwich, PHSnMWnABI, SPG2023 on June 14, 2023 by Kevin Thiel.

NUCAPS

Noticed the SHV special sounding was very similar to the NUCAPS sounding done an hour later. NUCAPS on the left and SHV on the right. The surface and near surface environment did not match as well.

OCTANE

Neat to see OCTANE highlight the taller clouds that are developing behind the main storm activity over the western CWA. Lightning Cast started highlighting this area too for a lightning threat.

Very nice divergent signature on the updraft. However, the 80 kts of divergence seems underdone given the MESH of 1.51”. I know the speeds are dependent on the environmental winds, but just seemed odd given the hail potential. Calibration would be helpful to help determine the hail size potential based on updraft divergence.

OCTANE captured two updrafts from a splitting storm over LZK’s CWA. This helped to see the potential split earlier than when viewable on Radar.

Here is when OCTANE first denoted the split vs. what radar had at the same time.

PHS

Handled the storm location and timing rather well at the start of the exercise for SHV.

Noticed for the LZK CWA PHS was about 2-3 hours early with the storm activity, but had the location correct. Radar image at 21z, PHS image at 19z

– Rainman

BMX Severe Thunderstorms

Posted in DSS, LightningCast, OCTANE Speed Sandwich, PHSnMWnABI, ProbSevere, SPG2023 on June 14, 2023 by Kevin Thiel.

Overall, I used OCTANE, PHS, ProbSevere 3 and LtgCast today. NUCAPS wasn’t really accessible. Worked the DSS event, an Air Show, which was canceled due to severe thunderstorms all afternoon producing tornadoes, large hail and damaging winds. DSS for this event would have been done days ago.

Below is a shot of LtgCast on a radar background and ELN measured lightning, the +/- are positive and negative ground strokes, and the cyan dots are in-cloud. It is interesting how the 75% probs lead out into southwestern Georgia though the showers there are more stratified and lightning isn’t expected, yet it gave about 45 minute notice of lightning strikes; that’s a good thing. But how useful is this? It predicted a few single lightning strikes tens of miles apart scattered across 100 miles which isn’t really useful; would you stop all outdoor activities across ¼ of Georgia for a few stray strikes? Would you clear the baseball field because a lightning strike will hit in the next hour somewhere within 50 miles? Not likely, but knowing there is some chance is valuable information for an event coordinator for risk analysis. If they can make minor changes to activities with little or no impacts, it helps, especially if it’s an area where lightning isn’t expected. What would be a big plus would be an estimate of flash density/frequency expected to go with the probs. That gets back to tracking the convective cells to predict areas of dense lightning. We have radar and ELN’s for that.

PHS composite reflectivity vs radar at 21Z… I find little value in the PHS composite reflectivity product. Below you see PHS composite reflectivity compared to the radar returns at 21Z. It’s not doing too well and I haven’t seen a time when it has done well predicting where the storms will be. The HRRR, NSSL WARF, HRef, NAM Nest and other high res models do much better.

PHS Bulk Shear 0-1 km below on the left and 0-3 km below on the right both show a line between areas of lower and higher shear along the boundary where the severe storms were tracking, but this occurred after the convection started. I don’t see a pre convection signal pointing to where the training storms formed.

The Bulk Shear 0-6 km below shows more promise with the 19Z frame showing a boundary where the training severe storms formed/tracked (what did it look like at 16Z or 17Z?). I would need to see more of this pre convection to really make a judgment, and would need to see positive validation/verification to have any confidence in it as a tool.

– Super Bolt

PHS Reflectivity Forecast Helping Out with DSS

Posted in DSS, LightningCast, PHSnMWnABI, ProbSevere, SPG2023 on June 14, 2023 by Kevin Thiel.

The Panda Ceremony was held at the Jackson, MS Zoo on the evening of Wednesday, Jun 14, 2023. Strong to severe storms were forecast throughout the afternoon and evening hours and the event coordinator requested DSS for lightning and any severe weather with as much lead time as possible. Using the 14.16z initialization of the PHS reflectivity was useful in providing some timing details to the event coordinator (See Figure 1). It suggested a fairly robust storm to roll through the Jackson area by around 00z with the forecast reflectivity ranging from 50-65 dBz directly over the event site.

The reflectivity forecast did well with depicting a fairly large storm to move across southern Mississippi but was a bit too north on the location. Overall, the product was very useful in boosting the forecaster’s confidence in the convection timing to impact the event. See Figure 4 for a look a the verification.

Figure 1: Loop of the 14.16z PHS layer reflectivity had a large storm over Jackson, MS, and impact the event (black range ring) by 00z.

Figure 2: A DSS Graphic was issued shortly after 3 p.m. to highlight the timing and potential impacts of the Panda Ceremony. The original image had the animated GIF above with the PHS reflectivity forecast.

Figure 3: This was the first of 3 graphics created for the event and this graphic highlighted the severe weather threat and timing. Overlaid is the MRMS reflectivity greater than 35 dBz and OCTANE Winds.

Figure 4: A loop of MRMS with ProbSevere and LightningCast shows some verification of the PHS reflectivity forecast shown above. This loop ends at 2232z.

– Podium

Day 3 Review of Products & Operational Applications

Posted in OCTANE Speed Sandwich, PHSnMWnABI, ProbSevere, SPG2023 on June 14, 2023 by Kevin Thiel.

I took on the warning forecaster role during the operational period today. A supercell was underway at the start of the period, so I began by issuing a Severe Thunderstorm Warning. ProbSevere was (unsurprisingly) indicating a slam dunk for severe wind and large hail (Figure 1) but I noticed when sampling the ProbSevere data that MESH was slow to pick up on just how large the hail was with this storm. A broadcast meteorologist passed along a report of 5-inch hail at 2000z, but MESH did not indicate 4+ inch hail until 2020z.

Figure 1

I also noticed that PHS composite reflectivity was much too slow with the progression of convection across the SHV CWA. Below are a screenshot of PHS progged composite reflectivity at 21z and a screenshot of the radar 0.3 degree reflectivity at 21z. PHS expected the supercell of interest to still be located over the northeast portion of SHV (Figure 2) while in reality the supercell was about to exit the easternmost fringes of the CWA (Figure 3).

Figure 2

Figure 3

Once the aforementioned supercell exited the SHV CWA, we pivoted to the LZK CWA to monitor the ongoing convection there. I decided to interrogate the OCTANE products because I hadn’t looked at much satellite imagery thus far.

OCTANE was especially useful in two ways today:

OCTANE Speed indicated a storm split underway as two speed maxima can be seen in the red-orange hues (Figure 4, top left panel)
I tweaked the AWIPS colormap for OCTANE Direction to better depict the storm-top divergence occurring (Figure 4, top right panel)

Figure 4

– Vort Max

Verification of NUCAPS Soundings

Posted in DSS, NUCAPS, SPG2023 on June 14, 2023 by Kevin Thiel.

Using the 1930z pass of the NUCAPS soundings during an SPC Moderate Risk was quite exciting. The environment was primed for significant severe weather and having NUCAPS soundings available at the time of convection out of ahead of storms was beneficial. It provided additional confidence in the severity of the environment.

As you can see from the satellite, soundings were unusable further north due to the ongoing convection and cloud cover. Thankfully clear skies prevailed from Jackson and southeastward providing some impressive sounding data to compare to SPC Mesoanalysis. Sounding A was well in the warm sector and sunny skies and thus had the highest CAPE values and lapse rates. Sounding B was just to the southwest of the DSS event and was beginning to see some anvil over that location, but it still provided reasonable data and compared well with SPC mesoanalysis.

Figure 1: Location of the NUCAP Soundings chosen to view and compare to SPC mesoanalysis. For reference, the range rings outline the 5 and 10-mile radius around a DSS event in Jackson, MS.

Figure 2: Sounding A with a surface-based CAPE of 6004!

Figure 3: Sounding B with a modest 4079 surface-based CAPE.

Figure 4: SPC mesoanalysis Surface-Based CAPE and CIN at 20z on June 14, 2023. The star is the DSS event location and the two dots are the estimated location of the soundings analyzed.

Figure 5: SPC Mesoanalysis 0-3km lapse rate (C/km) depicted lapse rates from 7.0-8.0. Once again, both soundings matched up well with SPS data.

– Podium

BMX Warning Met (West Sector) on June 14, 2023

Posted in ProbSevere, SPG2023 on June 14, 2023 by Kevin Thiel.

Our group role played as BMX during an anomalously conducive environment for severe weather consisting of very high instability and very high shear. My position was warning met, sectorized for the western half of the CWA.

ProbSevere helped considerably in triaging which storms deserved attention, and which storms were trending in such a way that warranted a warning decision and/or adjustment. A combination of several supercells that would merge with other cells and evolve into clusters and bowing quasi-linear structures made it difficult to have a comfortable handle on storm behavior and associated hazards. This was compounded by the fact that radar data from the favored radar site, KBMX, was dropping out at times. While other datasets were referenced (satellite, surface observations, storm reports, objective analysis, etc.), ProbSevere felt like it gave the biggest helping hand in warning decisions during this complex scenario.

Looking in the southwest portion of the CWA around 20:30 – 22:00 UTC, ProbSevere signaled the diminishing probabilities associated with a bowing segment that earlier resulted in an 82 mph wind gust within eastern MS as convection was decaying rapidly. This helped grow confidence in holding off on a warning as it entered BMX’s CWA.

ProbSevere also pointed at a cluster of storms increasing in potential for severe hazards. This was helpful given the noisy velocity data, higher than desired sample height (closest radar sampled ~5-8kft), and likely complications regarding wind vectors having some orthogonal component to the radar radial. Essentially, ProbSevere provided clarity and continuity in a noisy radar situation increasing confidence in storm behavior.

Having discussion with a developer, I expressed how useful it was to not only have a time series to view trends in overall probabilities of severe hazards, as well as of each hazard (i.e. hail, wind, tornado), but also time series of the data that drives the probabilities like those offered by CIMSS.

The above time series corresponds to the cluster of storms in southwest BMX around 20:30 – 22:00 UTC (link). Notice in the time series the local minima in probabilities within ProbSevere v3 around 21:00 UTC (~47%) followed by a notable increase in probabilities, exceeding 80% around 20 minutes later. This trend in local minima followed by increasing probabilities was more obvious than ProbSevere v2. Looking at the individual inputs, this was likely driven by an increase in things like Azimuthal Shear, VIL, MESH, Lightning attributes, along with other environmental attributes.

– 0SMBLSN

6/14/23 HWT – SHV

Posted in LightningCast, NUCAPS, OCTANE Speed Sandwich, PHSnMWnABI, ProbSevere, SPG2023 on June 14, 2023 by Kevin Thiel.

Operational window encompassed ongoing severe storms at the start of the period which moved eastward out of the CWA by mid afternoon. The resultant outflow boundary / cold front intersection to the west of the CWA become the focus regions for potential for renewed storm development.

NUCAPS 6/14/23 19z sounding south of the outflow boundary of interest compared to nearby surface observation showed a large discrepancy in observed surface conditions (90/72 at nearby ASOS). This raises considerable questions on how these soundings are to be best utilized in operations.

OCTANE was useful in monitoring the attempted updrafts along the outflow boundary. It seems to show updraft growth more clearly than the day cloud phase product. I would like to see these data incorporated into the LightningCast model as this product is also very good at highlighting potential areas for CI.

OCTANE output was also viewed in a region of a splitting supercell across western AR. Good conversation with developers on further development of the wind retrievals with observational data constructed hodographs being an operational request.

Utilized LightningCast to highlight the region of concern for new storm development. The storms did develop but it was a more gradual evolution. The highlighted region did verify as the region of development.

ProbSevere did a great job as a safety net for radar warning operations. The element trend window is a helpful addition. Talked with the developer on potential marking times along the time series where the element changes ID or grows in area to show when ProbSevere has merged or separated elements as this impacts resultant probabilities.

PHS model output from the 16z run was viewed online and compared to the corresponding HRRR. At the time of the exercise conclusion its solution had verified better on composite reflectivity than did the HRRR. A product in AWIPS highlighted regions where the fusion data is different than a zero hour model output would be beneficial for situational awareness and potentially for model output utilization.

– jbm